Method of igniting gas or vapor discharge spaces



Oct.- 25, 1938.

G. MIERDEL 2,134,527 METHODOF IGNITING GAS OR VAPOR DISCHARGE SPACESFiled Co t. 50, 935 2 Sheets-Sheet 1 R M W w. 6

WITNESSES:

ATTORNE Get. 25, 1938.

G. MIERDEL 2,134,527 METHOD OF IGNITING GAS OR VAPOR DISCHARGE SPACESFiled Oct. so, 1955 2Sheets-Sheet 2 F1 .2. F/ .6.

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ATTORNEY Patented Oct. 25, 1 938 "PATENT OFFICE METHOD OF IGNITING GASon VAPO DISCHARGE SPACES Georg Mierdel, Berlin-Siemensstadt, Germany,

assignor to Siemens-Schuckertwerke Aktiengesellschaft,Berlin-Siemensstadt, Germany, a

corporationof Germany Application October so, 1935, Serial No.47 ,49s

In Germany January 23, 1935 14 Claims. (01. 250-275) verters,converters, or the like. According to the invention, the potential ofthe anode of the discharge spacewhich is to be ignited and thegrid ofwhich is connected to a blocking potential, is

' for a short interval of time reduced at least approximately to thepotential of the cathode. Accordingly, the discharge space is, as in theusual applications of controlled rectifiers, provided with an auxiliaryelectrode which operates on the dis-- ,charge path between the anode andthe cathode.

: The auxiliary electrode preferably has the form of ,a control grid andthe control grid is permanently and without change connected to Such apotential that the discharge space is blocked; that; accordingly, apotential connected to the anode cannot without further change ignitethe discharge space. Other electrode structuresthan the usual controlgrids, for example, shells, which envelop the discharge path eitherwithin orwithout the container enclosingthe discharge space,

' may be utilized. As to the magnitudeuof the blocking potential whichis'tobe connected to the ,control grid, thedimensions of the dischargedevice utilized, and therefore particularly the dimensions of thecontrol electrode and the geometric dimensionsof the discharge spacebetween the cathode and the anode, are determining. For this purpose anegative direct current potential in series with a resistor inaccordance with the character of the discharge vesselutilized, isconnectedbetween the control electrode and the cathode. In many cases,however, the potential source may be dispensed with, i. e., the controlgrid may be connected to the cathode only through a resistor. The latterconnection is utilized only for thosevessels for which the so-calledignition characteristic line of the discharge vessel coincides with thecathode potential or lies in the positive region above it.

By experiment with the above characterized discharge spaces, it has beenestablished that the discharge space, which on the application of ananode potential (that may be either a direct cur rent or an alternatingcurrent potential) is under normal circumstances not ignited, may beignited ifby any means whatever the anode potential is for ashortinterval of time brought to the oathode potential or at leastapproximately to the cathode potential; For the purpose of changing theanode potential for a short interval of time, various means may beutilized For examplaa transformer may be connected in the anode circuit,in the secondaryof which a short'current impulse "is produced. Thetransformer is so connected that the potential peak introduced therebyin the anode circuit is opposite to the anode potential. Control meansof this type have, in the past, been utilized in rectifiers.Nevertheless the use has been heretofore in those rectifiers which, incontrast to the control method according to the invention, arenotignited by a potential decrease but by a momentary potential increase ofthe anode.

Another particularly advantageous means for reducing the anode to thecathode potential consists of a cap acitor connected'in parallel to thedischarge space through a switch whichis to be closed at the instantthedischarge space is to be ignited; The working potential impressedacross the discharge space is then short-circuitedthrough the capacitorand by the'cha'rg ing current of the g capacitor, the anode potential isfor a short interval of time reduced to a potential which isapproximately equal to the cathode potential. As the charge" onthecapacitor increases the anode potential rises immediately to its normaloperating value. in addition to again discharge the capacitor after thedischarge space is ignited thus to prepare it for the next ignition,forexample, in cases where the discharge space of a rectifier is to beperiodically ignited. For this purpose, a resistor is connected inparallel with thecapacitor. The magnitude of the resistor is such thatit does not disturb the decrease of the anode potential at the instantthat the capacitor circuit is connected in. The time constant of thecapacitor circuit determined by the capacitor and the resistor, however,must be sogauged that the discharge period of the capacitor is smallcompared to the period of ignition of the discharge space. In place of acapacitor with a parallel connected resistor, aresistor havingcharacteristic capacity (distributed capacity) of such magnitude thatthe parallel capacitor may be dispensed with, may be utilized.

' The invention may be utilized for the most diverse purposes. Forexample, a direct current network may be connected by the operation ofthe control method according to the invention. The switch lying in thecapacitor network is then preferably provided with two contacts whichare operated in succession. By the operation of the iirst"contactth'ecapacitor is connected in parallel tothe discharge space, While by thesecond contact the capacitor is short circuited for dis- Prefe'rably,means are provided charge purposes, preferably through a properlydimensioned resistor. Particularly important is the new control methodfor conversion arrangements which operate with controlled rectifiers,accordingly, for controllable rectifiers, inverters and converters. Inthese conversion arrangements, the time point of the ignition of thedischarge space is determined by the switching arrangement in thecapacitor circuit. For this purpose rotating switch apparatus, forexample, of the machine commutator type, are utilized as they have beenutilized heretofore with the usual grid controlled discharge paths.Mechanical contacts may be entirely avoided if auxiliary dischargespaces, particularly gas or vapor discharge spaces which are ignited bythe customary and well known means, are utilized in the capacitorcircuit for switching purposes. Gas or vapor discharge spaces arepreferable for the present use, tohigh vacuum electron tubes because theswitching load is practically unlimited, and because the capacitorcircuit must be switched in, above all else, without delay.

Fig. 1 is a diagrammatic view of an embodiment of my invention,

Fig. 2 is a diagrammatic view of a modification of my invention, 1

Fig. 3 is a diagrammatic view showing another modification of myinvention,

Fig. 4 is a diagrammatic view showing a further modification of myinvention,

Fig. 5 is a diagrammatic view showing a still further modification of myinvention,

Fig. 6 is a diagrammatic view of a circuit which is electricallyequivalent to the Fig. 1 circuit and which is used in explaining theoperation of my invention, and

. Fig. '7 is a graph illustrating the operation of the circuit shown inFig. 6.

In Fig. 1, the connection for a controllable rectifier is illustrated asan embodiment of the invention. A mercury vapor discharge vessel l is inthe known manner provided with an anode 2, a control grid 3 and amercury cathode 4, and by the operation of an auxiliary electrode 5, apermanently-burning excitation arc is maintained. The control grid 3 isconnected to the cathode through a battery 6 and a resistor T. Thebattery 6 may be dispensed with, as has been mentioned before, if thedischarge vessel is of such character that the connection between thecontrol grid and the cathode sufiices to block the discharge. Thisarrangement has the advantage that the connection conductors l6 (Fig. 5)be-- tween the control grid and the cathode may be disposed within thedischarge vessel so that the separate bushings for the grids such as arenecessary in the known grid controlled discharge devices may beeliminated.

A capacitor 8 is according to the invention connected in parallel withthe discharge space of the discharge vessel. The capacitor may beconnected and disconnected by a switching device 9 which is to beperiodically actuated. The capacitor 8 is shunted by a dischargeresistor Ill.

The alternating current source II is connected to the discharge vessel Ithrough the current consumption load I2. The discharge vessel operatesas a rectifier, the current transmission of which or the mean potentialdelivered by which may be regulated with the aid of the switchingapparatus 9. In place of the switch 9, an auxiliary discharge device I8(Fig. 2) which is periodically ignited may be utilized as has beenexplained before.

The arrangement may, moreover, be improved by connecting an inductor ISin the anode circuit as viewed from the load side before the connectionof the capacitor parallel circuit. The inductor prevents the potentialof the anode from being raised sooner than is desired by the currentflowing out of the load circuit or out of the feeding source when thecapacitor is connected In Fig. 3 a transformer in the secondary 22 ofwhich a short current impulse is produced is shown as connected in theanode circuit. The transformer is so connected that the potential peakintroduced thereby in the anode circuit is opposite to the anodepotential.

In the Fig. 4 modification a switch 24 with two contacts 26 and 28 isshown in the capacitor circuit. The'contacts 26 and 28 are operated insuccession. By the operation of the first contact 26, the capacitor isconnected in parallel to the :1

discharge space I, while by the second contact 28 the capacitor is shortcircuited, preferably through a properly dimensioned resistor 30.

The theory of operation of the apparatus is illustrated in Figs. 6 and'7. A thyratron S may be regarded as connected through an ohmic resistorR and an inductor L (leakage inductance, inductance of the conductors,etc.), to a direct current source with the potential U0. The gridpotential may be assumed to be so low that the tube does not, itself,become ignited. According to the invention applied for, an ignition isto be effected by the actuation of a suitable switch mechanism by theoperation of which the anode is connected to the capacitor C which isnormally 0 maintained without a difference of potential by a parallelconnected resistor. The above method is based on the following theory:

By closing the above-mentioned switch, the anode potential is suddenlyreduced to zero.

However, this does not correspond to the equilibrium condition andfurthermore in the final condition, the anode must again take on thepotential U0 of the potential source. This takes place in general,however, in the form of oscillations which, disregarding damping,increase the anode potential to twice its normal value, 1. e.,t0 2Uoafter the first half wave of the anode potential. By this means, anignition may now be effected at least in the case in which the staticgrid potential no longer suffices to prevent the ignition for asubstantial over-potential.

In addition to this possible explanation, there is another point whichmust be brought in particularly when, as may be realized experimentally,the method operates in the case in which the grid potential is lowenough to block for double the anode potential. This point relates tothe variation of the grid potential by reason of the capacitive effectof the anode potential. The measure of this is the time constant of thegrid circuit given by the capacity between grid and cathode and theseries resistor of the grid. If this time constant is very large, thegrid potential varies in proportion with the anode potential and may,therefore, take on a value which is not sufiicient for blocking thedischarge when the anode potential rises. In general, however, the timeconstant of the grid circuit will be smaller than the oscillation periodof the anode circuit. Also in such a case, the effective grid potentialis greater than the static value, as simple consideration will show,during the rise of the anode potential and accordingly during the Wholeof the first half Wave of the circuit closing oscillation, so that inthis case there is also the possibility of ignition.

The proposed explanation possibilities also naturally are applicable ifthe potential U0 is an alternating current potential, as is the case forcontrolled discharge tubes.

The invention has a series of important advantages over the knowncontrollable electric discharge spaces. All interlocking of the circuitby control electrodes of the discharge path disappears. The control gridmay even, under certain circumstances, be connected with one of theother electrodes within the discharge container, so

that no bushing leading to the outside is necessary. Compared to othercontrol devices in which the anode potential is varied for purposes ofignition, the invention has the advantage that the potential is notincreased but decreased. -As

the description of the invention shows, no additional auxiliary sourcesare necessary for operation.

I claim as my invention:

1. Method of igniting a gas or vapor discharge device connected in acircuit having distributed impedance .particularly for the purpose ofcontrol of a rectifier which comprises reducing the potential of theanode of the discharge device, to the grid of which a blocking potentialis connected, for a short interval of time, at least approximately tothe potential of the cathode for producing an interelectrode potentialimpulse to ignite said device.

2. Method according to claim 1 characterized by the fact that acapacitor connected in parallel with the discharge space is connected inat the instant of ignition.

3. Apparatus according to claim 1 characterized by the fact that, by theoperation of a transformerlying in the anode circuit a potential impulseopposite to the anode potential is produced at the instant of ignition.

4. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes, saiddischarge device being connected in a circuit having distributedimpedance, means for impressing a potential difference between saidprincipal electrodes, means for maintaining a potential differencebetween said control electrode and one of said principal electrodes thatis of such magnitude that said discharge device is normally deenergizedand means for momentarily connecting said principal electrodes toproduce an interelectrode' impulse for energizing said discharge device.

5. Apparatus according .to claim 4 characterized by the fact that thelast means includes a capacitor, which is to be momentarily connectedbetween the principal electrodes when the discharge device is to beenergized, said capacitor being shunted by a resistor.

6. Apparatus according to claim 4, character'- ized by the fact that thelast means includes a resistor with distributed capacity, which is to bemomentarily connected between the principal electrodes when thedischarge device is to be energized.

7. Apparatus according to claim 4, characterized by the fact that thelast means includes a capacitor circuit, which is to be momentarilyconnected between the principal electrodes when the discharge device isto be energized and a rotating contact device constructed in the mannerof a commutator for making the momentary connection.

8. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes, saiddischarge device being connected in a circuit having distributedimpedance, means for impressing a potential difference between saidprincipal electrodes, means for maintaining a potential differencebetween said control electrode and one of said principal electrodes thatis of such magnitude that said discharge device is normally deenergizedand means including an auxiliary discharge device for momentarilyconnecting said principal electrodes to produce an interelectrodeimpulse for energizing said discharge device.

9. Apparatus according to claim 4, particularly for working circuitswhich are connected in for comparatively large time intervals by thedischarge device which is to be ignited, characterized by the fact thatthe last means includes a capacitor circuit and a switch, with twocontacts to be successively actuated in the capacitor circuit, the firstof the switches connecting the capacitor in parallel to the dischargedevice while by the operation of the second of the switches thecapacitor is short circuited for discharge purposes.

10. Apparatus according to claim 4, characterized by the fact that thepotential difference between the control electrode and the one principalelectrode is zero and the conductor connecting the control electrode tothe one principal electrode is within the container of the dischargedevice.

11. Translating apparatus comprising an electric discharge device havinga control electrode and a plurality of principal electrodes, saiddischarge device being connected in a circuit having distributedimpedance, means for impressing a potential difference between saidprincipal electrodes, means for maintaining a potential differencebetween said control electrode and one of said principal electrodes thatis of such magnitude that said discharge device is normally deenergized,means including a capacitor circuit for momentarily connecting saidprincipal electrodes to produce an interelectrode impulse for energizingsaid discharge device and an inductor connected in the anode circuit ofsaid discharge device as viewed from the load circuit before theconnection of the capacitor circuit.

12. Apparatus according to claim 4 characterized by that the last meansincludes a capacitor, which is to be momentarily connected between theprincipal electrodes when the discharge device is to be energized.

13. Apparatus according to claim 4 characterized by that the last meansincludes a capacitor, which is to be momentarily connected between theprincipal electrodes when the discharge device is to be energized, and aresistor shunting said capacitor, the time constant of the capacitor andresistor network being small compared to the periodicity of thedifference of potential impressed between the principal electrodes.

14. Apparatus according to claim 4 characterized by that the last meansincludes a capacitor, and means for periodically connecting thecapacitor between said principal electrodes for a short interval 01'time to energize the discharge device.

GEORG MIERDEL.

